This invention relates to magnetic printing heads and in particular to high resolution magnetic printing heads in which the magnetic pole pieces are formed by electrodeposition.
A detailed description of magnetic printing is found in U.S. Pat. No. 4,097,871 issued to Berkowitz et al, said patent being assigned to the same assignee as herein, and the inventor herein being the same as one of the inventors in the aforementioned patent. It is to be particularly noted that the magnetic printing head described herein is a transverse magnetic printing head. That is to say, the direction of orientation of the magnetic field impressed on the recording medium is perpendicular to the direction of movement of the medium.
Magnetic printing basically involves the transfer of a dry magnetic ink image from a ferromagnetic recording medium to a permanent paper medium. A magnetic printing head selectively magnetizes regions of the ferromagnetic recording medium which, thereafter, attracts the magnetic ink. The ink is transferred to the recording medium by a magnetic ink brush thereby forming an image on the recording medium representative of the data desired to be transferred to the paper. The ink pattern on the recording medium is transferred to the paper medium on which the pattern is permanently fixed. The pattern on the magnetic recording medium is subsequently erased prior to the recording of new information thereon. The recording medium typically comprises a wide, flat belt having substantially the same width as the paper. The belt typically comprises a material similar to magnetic recording tape.
Magnetic printing offers several advantages over conventional printing methods. In particular, it is both rapid and relatively quiet. For example, magnetic printers are capable of printing speeds in excess of 6,000 lines per minute. Heretofore, however, the resolution attainable with magnetic printing has been limited to approximately 120 dots per inch. However, to achieve a print quality comparable to that of conventionally typewritten material, it is necessary to increase the resolution to 200 dots per inch (dpi) or more.
U.S. patent application Ser. No. 193,398, filed Oct. 2, 1980 (continuation-in-part of Ser. No. 060,921, filed July 26, 1979, now abandoned) describes a transverse magnetic head employing a long, comb-like structure, the teeth of which are oriented in a direction perpendicular to the direction of travel of the magnetic recording medium. This application is also assigned to the same assignee as the present invention and the inventor herein is one of the inventors in said application. The comb is composed of a material of high magnetic permeability so as to concentrate lines of magnetic flux at the tips of the comb teeth. A plurality of current carrying conductors is disposed through each of the gaps between the comb teeth and the current in these conductors controls the level of magnetic flux between the tips of adjacent comb teeth. The regions of magnetic flux, being in a position near to the magnetic recording medium, permit the selective magnetization of regions in the medium which regions thereafter attract magnetic ink. To achieve high resolution, the teeth of the comb must be spaced relatively close together. For example, if the teeth of the comb are spaced to form approximately 120 dots per inch, there is only a four mil spacing between adjacent teeth. Because of the small dimensions and the spacings involved, it does not appear practical to increase the resolution of the printing head simply by shrinking the spacing between the comb teeth.
There are several reasons for this practical limitation. First, even if the comb teeth could be more closely spaced, it becomes increasingly difficult to insert a magnetic comb with such fine teeth into a printed circuit board having equally finely spaced conductors for disposition between the comb teeth. Second, it becomes increasingly expensive to produce printed circuit boards having conductive pattern spacings of 200 lines per inch crossing an elongated gap in the printed circuit board as described in the aforementioned application, Ser. No. 060,921. Third, with decreased signal line dimensions, the resistance of the lines increases since they are significantly narrower. Accordingly, the line resistance is approximately doubled. This means that higher voltage circuit drivers are required, further increasing the cost of the printer. Fourth, by simply shrinking the dimensions, the dissipated power increases, thereby producing a potential heat problem particularly where the magnetic printing head contacts the recording medium. Dissipated power is also increased because of the greater duty cycle required in a 200 dot per inch magnetic printing head. However, in spite of the problems associated with increasing the resolution of the magnetic printing head disclosed in the abovementioned application Ser. No. 060,921, the teachings of this application, particularly those teachings related to digit line and word line patterns, are relevant to the present invention and therefore this application is incorporated herein by reference.
In U.S. Pat. No. 4,291,314, issued Sept. 22, 1981, to Nathan et al. and assigned to the same assignee as the present invention, the problems associated with inserting the high permeability magnetic comb structure in the printed circuit board assembly are obviated by the employment of electrodeposition methods to deposit high permeability magnetic material in the gaps between the signal conductors by electrodeposition. The electrodeposition of the magnetic material obviates the necessity of attempting to insert the comb into the printed circuit board without bending wires or breaking comb teeth because of the fragility of the parts occasioned by the requisite small dimensions. While the teachings of this invention avoid the problems of comb insertion, the problems of circuit cost and heat dissipation are nonetheless still present for printing heads having a resolution of 200 lines per inch or higher. Nonetheless, the above-noted U.S. Pat. No. 4,291,314 is relevant to the present invention with respect to its teachings concerning electrodeposition of the high permeability magnetic comb structure. Accordingly, U.S. Pat. No. 4,291,314 is incorporated herein by reference.